<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<style>
    .outer {
        width: 100%;
        height: 50px;
        display: flex;
    }
    .search-input {
        width: 100%;
        height: 100%;
        flex: 1;
        /*? 消除border占据content的影响*/
        box-sizing: border-box;
    }
    .search-button {
        width: 100px;
        height: 100%;
    }
</style>
<body>
<div class="outer">
    <input type="text" class="search-input" placeholder="Search" />
    <button class="search-button">Search</button>
</div>
</body>
</html>
